Metal-sulfur battery

ABSTRACT

Provided is a metal-sulfur battery, comprising a positive electrode material, a negative electrode material and an electrolyte, the positive electrode material comprises one of elemental sulfur and S-based compound; the electrolyte comprises a solvent and an electrolyte salt; and the electrolyte salt comprises one or more salts represented by structural formulas 1-3: 
     
       
         
         
             
             
         
       
         
         
           
             wherein, R 1  is selected from S or Se; R 2  is selected from C, Si, Ge or Sn; M 1  is selected from N, B, P, As, Sb or Bi; M 2  is selected from Li, Na, K, Ru, Cs, Fr, Al, Mg, Zn, Be, Ca, Sr, Ba or Ra; R 3  is selected from a carbon chain or an aromatic ring with part or all of hydrogen substituted by other elements or groups. The metal-sulfur battery provided by the disclosure can effectively solve the short circuit problem caused by metal dendrites on the negative electrode of existing metal-sulfur battery.

TECHNICAL FILED

The present disclosure belongs to the technical field of batteries, andin particular to a metal-sulfur battery.

BACKGROUND

With the advent of the 21st century, the energy problem is becoming moreand more serious, and the environmental pollution continues todeteriorate. In order to achieve sustainable development, theutilization and development of new energy and renewable energy hasbecome a hot research topic all over the world. Water energy, windenergy, hydrogen energy, nuclear energy, tidal energy and solar energyhave been vigorously developed and utilized all over the world. Theimprovement of the performance of energy storage devices can effectivelypromote the popularization of new energy applications. Among many energystorage devices, electrochemical energy storage battery has become oneof the important research directions in the world because of advantagesof high energy density, good energy conversion efficiency, lesspollution and convenient combination and movement.

Among all kinds of electrochemical energy storage batteries, thetheoretical energy density of elemental sulfur or sulfur-basedcomposite/metal battery is as high as 2600 Wh·Kg⁻¹, the actual energydensity can reach 300 Wh·kg⁻¹ at present, which may increase to around600 Wh·kg⁻¹ in the next few years. It is considered as one of the mostpromising secondary lithium battery systems at present. Alkali metallithium, sodium or potassium is used as negative electrode, which isvery likely to cause lithium, sodium or potassium to form a coating onthe surface of the negative electrode due to poor dynamic conditions ofthe negative electrode during low-temperature charging or high-ratecharging. With the growth of the coating, metal dendrites willeventually form. When the metal dendrites accumulate to a certainextent, they will contact the separator, which will cause extrusion andneedling on the separator, and eventually lead to mechanical failure ofthe separator and short circuit between the positive and negativeelectrodes. The generation of metal dendrites is an important factoraffecting the safety performance of batteries.

The existing method for solving the metal dendrites mainly utilizes aplurality of nano technologies to modify the lithium metal currentcollectors, including carbon ball structures, three-dimensional metalcurrent collectors and the like, but due to relatively complicatedprocess, the cost cannot be further reduced, and the performance is notremarkably improved, thus large-scale production cannot be realized;Secondly, the artificial SEI film generally has the problem of lowlithium ion conductivity, which does not meet the current demand forrapid charge and discharge. In recent years, a method for inhibiting thegrowth of lithium dendrites by effectively regulating the electrolytehas attracted much attention, which mainly solves the problem of unevenspace charge distribution caused by low-concentration lithium salts byincreasing the concentration of lithium salts in the electrolyte orpartly increasing the concentration lithium salts, thereby uniformizinglithium metal deposition and inhibiting the growth of lithium dendritesand the generation of dead lithium. Adding film-forming additives toelectrolyte with conventional lithium salt concentration is also aneffective means to inhibit lithium dendrites. The above-mentionedexisting technical means still can not solve the problem of metaldendrites of metal-sulfur battery.

In addition, when elemental sulfur is used as positive electrodematerial of lithium ion battery, the dissolution of the intermediateproduct lithium polysulfide (Li₂S_(n), 3≤n≤8) in the electrolyte leadsto the problems of low coulombic efficiency of the battery and lowutilization rate of active substances.

SUMMARY

The disclosure provides a metal-sulfur battery aiming at the shortcircuit problem caused by lithium dendrites grown on the metal lithiumof negative electrode in the existing metal-sulfur battery.

The technical solution of the present disclosure to solve the technicalproblems is as follows:

On one hand, the disclosure provides a metal-sulfur battery, comprisinga positive electrode material, a negative electrode material and anelectrolyte, the positive electrode material comprises one of elementalsulfur and S-based compound; the electrolyte comprises a solvent and anelectrolyte salt; and the electrolyte salt comprises one or more saltsrepresented by structural formulas 1-3:

wherein, R₁ is selected from S or Se; R₂ is selected from C, Si, Ge orSn; M₁ is selected from N, B, P, As, Sb or Bi; M₂ is selected from Li,Na, K, Ru, Cs, Fr, Al, Mg, Zn, Be, Ca, Sr, Ba or Ra; R₃ is selected froma carbon chain or an aromatic ring with part or all of hydrogensubstituted by other elements or groups.

According to the metal-sulfur battery provided by the presentdisclosure, the inventor has unexpectedly found that when one or moreelectrolyte salts represented by structural formulas 1-3 are applied tothe electrolyte of metal-sulfur battery, the effect of inhibiting thegrowth of metal dendrites on negative electrode is more than expected,and the battery cycle stability performance, the rate performance, thecoulombic efficiency, and the safety performance of the metal-sulfurbattery are effectively improved. By contrast, in conventional lithiumbattery systems such as lithium cobaltate/graphite, the electrolytecontaining the compounds represented by the above structural formulas1-3 does not show the above beneficial effects.

Optionally, the content of the electrolyte salt is 0.01M˜10M.

Optionally, in structural formulas 1-3, R₃ is selected from a saturatedcarbon chain containing 1-4 carbons, an unsaturated carbon chaincontaining 1-4 carbons or an aromatic ring, with part or all of hydrogensubstituted by a halogen element or a halogenated hydrocarbyl group.

Optionally, the electrolyte salt comprises one or more of the followingcompounds:

Optionally, the positive electrode material is a sulfur/carboncomposite. Preferably, the positive electrode material is a ketjenblack/sulfur composite.

Optionally, the electrolyte further comprises a nitrate, and the masspercentage of the nitrate is 0.1%-5% based on the mass of theelectrolyte being 100%.

Optionally, the negative electrode material comprises one or more ofelemental lithium, elemental sodium, elemental potassium, elementalaluminum and elemental magnesium.

Optionally, the metal-sulfur battery comprises a separator interposedbetween the positive electrode material and the negative electrodematerial.

Optionally, the metal-sulfur battery is a lithium-sulfur battery.

Optionally, the solvent is selected from one or more of a fluorinatedsolvent, ethylene glycol dimethyl ether, 1,3-dioxolane, propylenesulfite and methyl propionate.

According to the metal-sulfur battery provided by the presentdisclosure, the inventors have unexpectedly found that for ametal-sulfur battery using one or more of a fluorinated solvent,ethylene glycol dimethyl ether, 1,3-dioxolane, propylene sulfite, andmethyl propionate as a solvent, the addition of one or more electrolytesalts represented by structural formulas 1-3 can inhibit the dissolutionof sulfur in positive electrode material of the metal-sulfur batteryduring charging and discharging.

Optionally, the fluorinated solvent comprises one or more offluoroethylene carbonate, 3,3,3-fluoroethyl methyl carbonate and1,1,2,2-tetrafluoroethyl-2′,2′,2′-trifluoroethyl ether.

Optionally, the electrolyte salt further comprises one or more of LiPF₆,LiBF₄, LiBOB, LiClO₄, LiCF₃SO₃, LiDFOB, LiN(SO₂CF₃)₂ and LiN(SO₂F)₂.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph of cycle performances of the metal-sulfur batterieswith different electrolytes at 1 C current density provided byEmbodiment 1 and Comparative example 1 of the present disclosure;

FIG. 2 is a graph of cycle performances of the metal-sulfur batterieswith different electrolytes at 2 C current density provided byEmbodiment 1 and Comparative example 1 of the present disclosure;

FIG. 3 is a graph of cycle performances of the batteries provided byEmbodiment 20 and Comparative example 17 of the present disclosure;

FIG. 4 is a graph of cycle performances of the batteries at 0.5 Ccurrent density provided by Embodiment 24 and Comparative example 17 ofthe present disclosure;

FIG. 5 is a graph of cycle performances of the batteries at 1 C currentdensity provided by Embodiment 24 and Comparative example 17 of thepresent disclosure;

FIG. 6 is a comparative diagram of the interface impedance of thelithium metal of the half batteries provided by Embodiment 26 andComparative example 18 of the present disclosure;

FIG. 7 is a charge-discharge curve of the lithium metal of the halfbatteries provided by Embodiment 26 and Comparative example 18 of thepresent disclosure;

FIG. 8 is a partial enlarged view of FIG. 7;

FIG. 9 is a cycle curve of coulombic efficiency of the half batteryprovided by Embodiment 26 of the present disclosure;

FIG. 10 is a comparative diagram of the interface impedance of thelithium metal of the half batteries provided by Embodiment 27 andComparative example 19 of the present disclosure;

FIG. 11 is a cycle curve of coulombic efficiency of the half batteryprovided by Embodiment 27 of the present disclosure;

FIG. 12 is a comparative diagram of the interface impedance of thelithium metal of the half batteries provided by Embodiment 28 andComparative example 20 of the present disclosure;

FIG. 13 is a cycle curve of coulombic efficiency of the half batteryprovided by Embodiment 28 of the present disclosure;

FIG. 14 shows pictures of the electrode pole piece, TEM and EDX of themetal-sulfur batteries with different electrolytes provided byEmbodiment 1 and Comparative example 1 of the present disclosure afterbeing charged and discharged for 5 times;

FIG. 15 shows pictures of the separators of the metal-sulfur batterieswith different electrolytes provided by Embodiment 29 and Comparativeexample 21 of the present disclosure after being charged and dischargedfor 5 times;

FIG. 16 shows pictures of the separators of the metal-sulfur batterieswith different electrolytes provided by Embodiment 30 and Comparativeexample 22 of the present disclosure after being charged and dischargedfor 5 times;

FIG. 17 shows pictures of the separators of the metal-sulfur batterieswith different electrolytes provided by Embodiment 31 and Comparativeexample 23 of the present disclosure after being charged and dischargedfor 5 times;

FIG. 18 shows pictures of the separators of the metal-sulfur batterieswith different electrolytes provided by Embodiment 32 and Comparativeexample 24 of the present disclosure after being charged and dischargedfor 5 times;

FIG. 19 shows pictures of the separators of the metal-sulfur batterieswith different electrolytes provided by Embodiment 33-36 and Comparativeexample 1 of the present disclosure after being charged and dischargedfor 5 times;

DETAILED DESCRIPTION OF THE DISCLOSURE

In order to make the technical problems to be solved, technicalsolutions and beneficial effects provided by the present disclosureclearer, the present disclosure will be further described in detail withreference to the drawings and embodiments. It should be understood thatthe specific embodiments described herein are only used to explain thepresent disclosure, not intended to limit the present disclosure.

An embodiment of the present disclosure provides a metal-sulfur battery,including a positive electrode material, a negative electrode materialand an electrolyte, the positive electrode material comprises one ofelemental sulfur and S-based compound; the electrolyte comprises asolvent and an electrolyte salt; and the electrolyte salt comprises oneor more salts represented by structural formulas 1-3:

wherein, R₁ is selected from S or Se; R₂ is selected from C, Si, Ge orSn; M₁ is selected from N, B, P, As, Sb or Bi; M₂ is selected from Li,Na, K, Ru, Cs, Fr, Al, Mg, Zn, Be, Ca, Sr, Ba or Ra; R₃ is selected froma carbon chain or an aromatic ring with part or all of hydrogensubstituted by other elements or groups.

One or more electrolyte salts represented by structural formulas 1-3 areapplied to the electrolyte of metal-sulfur battery, the effect ofinhibiting the growth of metal dendrites on negative electrode is morethan expected, and the battery cycle stability performance, the rateperformance, the coulombic efficiency, and the safety performance of themetal-sulfur battery are effectively improved.

In some embodiments, the content of the electrolyte salt is 0.01M˜10M,preferably 0.1M˜5M.

In a more preferred embodiment, the content of the electrolyte salt is0.1M˜2M.

In some embodiments, in structural formulas 1-3, R₃ is selected from asaturated carbon chain containing 1-4 carbons, an unsaturated carbonchain containing 1-4 carbons or an aromatic ring, with part or all ofhydrogen substituted by a halogen element or a halogenated hydrocarbylgroup

In some embodiments, the electrolyte salt includes one or more of thefollowing compounds:

In some embodiments, the solvent includes one or more of ethylene glycoldimethyl ether (DME), dimethyl carbonate (DMC), 1,3-dioxolane (DOL),vinylene carbonate (VC), propylene carbonate (PC), ethylene carbonate(EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC),fluoroethylene carbonate (FEC), propylene sulfite (PS) and methylpropionate (PA).

Preferably, the positive electrode material is a sulfur/carboncomposite. More preferably, it is a ketjen black/sulfur composite.

In a more preferred embodiment, the solvent is a mixture of1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME).

Specifically, in the solvent, the mass ratio of 1,3-dioxolane (DOL) toethylene glycol dimethyl ether (DME) is 0.1˜10. In a more preferredembodiment, the mass ratio of 1,3-dioxolane (DOL) and ethylene glycoldimethyl ether (DME) is 1:1.

In some embodiments, the electrolyte further includes a nitrate, and themass percentage of the nitrate is 0.1%˜5% based on the mass of theelectrolyte being 100%.

Through a large number of experiments, the inventors found that thenitrate and electrolyte salts represented by structural formulas 1-3 canbe used together to improve the cycle performance of the battery moreeffectively.

In some embodiments, the negative electrode material comprises one ormore of elemental lithium, elemental sodium, elemental potassium,elemental aluminum and elemental magnesium.

In a preferred embodiment, cations in the nitrate are selected from thesame metal elements as the negative electrode material, and when thenegative electrode material is selected from Li, the nitrate is selectedfrom LiNO₃; when the negative electrode material is selected from Na,the nitrate is selected from NaNO₃; and when the negative electrodematerial is selected from K, the nitrate is selected from KNO₃.

In a preferred embodiment, in structural formulas 1-3, M₂ is selectedfrom the same metal element as the negative electrode material, and whenthe negative electrode material is selected from Li, M₂ is selected fromLi⁺; when the negative electrode material is selected from Na, the M₂ isselected from Na⁺; when the negative electrode material is selected fromK, M₂ is selected from K⁺.

In some embodiments, the metal-sulfur battery further includes aseparator interposed between the positive electrode material and thenegative electrode material.

The metal-sulfur battery provided by the embodiment of the presentdisclosure can effectively inhibit the growth of metal dendrites on thenegative electrode because of containing the above electrolyte, and hasbetter battery cycle stability, rate performance, coulombic efficiencyand safety performance.

In a preferred embodiment, the metal-sulfur battery is a lithium-sulfurbattery.

In some embodiments, the solvent is selected from one or more of afluorinated solvent, ethylene glycol dimethyl ether, 1,3-dioxolane,propylene sulfite and methyl propionate.

According to the metal-sulfur battery provided by the presentdisclosure, the inventors have unexpectedly found that for ametal-sulfur battery using one or more of a fluorinated solvent,ethylene glycol dimethyl ether, 1,3-dioxolane, propylene sulfite, andmethyl propionate as a solvent, the addition of one or more electrolytesalts represented by structural formulas 1-3 can inhibit the dissolutionof sulfur in positive electrode material of the metal-sulfur batteryduring charging and discharging.

In some embodiments, the solvent is selected from two of a fluorinatedsolvent, ethylene glycol dimethyl ether and 1,3-dioxolane. Preferably,the volume ratio between them is 1:2-2:1.

In some embodiments, the fluorinated solvent comprises one or more offluoroethylene carbonate, 3,3,3-fluoroethyl methyl carbonate and1,1,2,2-tetrafluoroethyl-2′,2′,2′-trifluoroethyl ether.

In some embodiments, the electrolyte salt further comprises one or moreof LiPF₆, LiBF₄, LiBOB, LiClO₄, LiCF₃SO₃, LiDFOB, LiN(SO₂CF₃)₂ andLiN(SO₂F)₂.

The present disclosure will be further explained by the followingembodiments.

Embodiment 1

The embodiment is used for explaining the metal-sulfur battery and thepreparation method thereof disclosed by the disclosure, and includes thefollowing steps:

Preparation of battery: Sulfur and Ketjen Black were mixed at a massratio of 1:3, and heated at 155° C. for 12 hours to obtain C/S compositewith sulfur content of 66%. The composite was mixed with 10 wt %PVDF-NMP solution, and the mixed slurry was coated on aluminum foil,dried in vacuum at 60° C. for 12 hours, and then cut into wafers with adiameter of 12 mm, which were used as the positive electrode of buttoncell. The separator was celgard 2325, and the negative electrode waslithium sheet with a diameter of 16 mm and a thickness of 0.4 mm. Theamount of electrolyte was 20 ul/mgS, and the electrolyte was selectedfrom electrolyte A.

Electrolyte A: 1M lithium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide was dissolved in thesolvent of DOL:DME=1:1, and then 1 wt % of LiNO₃ was added as additiveto obtain a battery electrolyte, labeled LiHFDF.

Comparative Example 1

This comparative example is used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, it was the same as Embodiment 1 except that:

the electrolyte is selected from electrolyte B.

Electrolyte B: 1M lithium bistrifluoromethanesulfonimide was dissolvedin the solvent of DOL:DME=1:1, and then 1 wt % of LiNO₃ was added asadditive to obtain a battery electrolyte, labeled LiTFSI.

Embodiments 2-25

Embodiments 2-25 are used to illustrate the metal-sulfur battery and itspreparation method disclosed in the present application, they were thesame as Embodiment 1 except that: the adopted positive electrodematerial, negative electrode material, electrolyte solvent andelectrolyte additive are shown in Embodiments 2-25 of Table 1.

Comparative Example 2-17

Comparative example 2-17 are used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, they were the same as Embodiment 1 except that:

the adopted positive electrode material, negative electrode material,electrolyte solvent and electrolyte additive are shown in Comparativeexample 2-17 of Table 1.

Embodiment 26

The embodiment is used to explain the metal-sulfur battery and thepreparation method thereof disclosed by the disclosure, and includes thefollowing steps:

(1) lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (abbreviatedas LiHFDF) was added into an aluminum can as lithium salt, whereinLiHFDF was purchased from TCI company, and the purity was 98%; then 3 mLsolvent of DME:DOL=1:1 vol % was added into the aluminum can with apipette, then the aluminum can was sealed and placed on a magneticstirring table and stirred for 12 hours until lithium salt dissolved toobtain electrolyte, the magnetic stirring temperature was controlled at30° C. for 12 h, the LiHFDF concentration was 1M, and 1% lithium nitratewas added, the whole preparation process of electrolyte was carried outin a glove box with argon atmosphere, and the water content was <1 ppm,oxygen content was <1 ppm;

(2) a 2025 button battery was prepared using the electrolyte obtainedfrom step 1, the 2025 button battery was assembled using a copper foilwith a diameter of 16 mm as counter electrode and a lithium metal sheetof 16 mm, and the separator of the 2025 button battery was PP2400, witha diameter of 19 mm.

Embodiment 27

Embodiment 27 is used to illustrate the metal-sulfur battery and itspreparation method disclosed in the present application, it was the sameas Embodiment 26 except that:

In the first step, the solvent adopted was DMC:EC:DEC=1:1:1 vol %.

Embodiment 28

Embodiment 28 is used to illustrate the metal-sulfur battery and itspreparation method disclosed in the present application, it was the sameas Embodiment 26 except that:

In the first step, the adopted lithium salts were LiHFDF and LiTFSI, andthe concentration of LiHFDF was 0.2M, and the concentration of LiTFSIwas 1M.

Comparative Example 18

Comparative example 18 is used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, it was the same as Embodiment 26 except that:

In the first step, LiTFSI was adopted as lithium salt to replace LiHFDFof Embodiment 26, and the concentration of LiTFSI was 1M.

Comparative Example 19

Comparative example 19 is used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, it was the same as Embodiment 27 except that:

In the first step, LiTFSI was adopted as lithium salt to replace LiHFDFof Embodiment 27, and the concentration of LiTFSI was 1M.

Comparative Example 20

Comparative example 20 is used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, it was the same as Embodiment 28 except that:

In the first step, the electrolyte did not include LiHFDF.

Performance Test

1. Test the cycle performance of the metal-sulfur batteries prepared byEmbodiment 1 and Comparative example 1. The test results are shown inFIG. 1 and FIG. 2. The four groups of data from top to bottom in FIG. 1are coulombic efficiency data of Embodiment 1, coulombic efficiency dataof Comparative example 1, battery capacity data of Embodiment 1 andbattery capacity data of Comparative example 1 at 1 C current density.The four groups of data from top to bottom in FIG. 2 are coulombicefficiency data of Embodiment 1, coulombic efficiency data ofComparative example 1, battery capacity data of Embodiment 1 and batterycapacity data of Comparative example 1 at 2 C current density.

It can be seen from FIG. 1 that when the electrolyte provided by thepresent disclosure was used in Embodiment 1, the first dischargecapacity of the battery was 695 at a current density of 1 C (1675mAg⁻¹), after 700 cycles, the battery capacity could still be maintainedat 490 mAhg⁻¹, and the capacity fade of each cycle was 0.04%; incontrast, Comparative example 1 used the electrolyte with LiTFSI(Lithium bistrifluoromethanesulfonimide) as lithium salt, its firstdischarge capacity was 690 mAhg⁻¹, after 700 cycles, the batterycapacity was 190 mAhg⁻¹, and the capacity fade of each cycle was 0.1%.In addition, after 700 cycles, the coulombic efficiency of themetal-sulfur battery provided by Embodiment 1 could still maintain at97%, while the coulombic efficiency of the metal-sulfur battery providedby Comparative example 1 decreased to about 92% after 700 cycles. It canbe seen from FIG. 1 that the electrolyte provided by the presentdisclosure can effectively improve the cycle stability and coulombicefficiency of the metal-sulfur battery.

As can be seen from FIG. 2, when the current density was 2 C, the resultwas similar to that when the current density was 1 C.

2. Test the batteries prepared by Embodiment 20 and Comparative example17 for 500 cycles at a current density of 0.5 C, and the results areshown in FIG. 3.

It can be seen from FIG. 3 that when the current density was 0.5 C, thecapacity of the battery could reach 628 mAhg⁻¹ after 200 cycles whenusing 1M LiHFDF electrolyte without adding lithium nitrate, and thebattery capacity quickly decreased to 363 mAhg⁻¹ after 200 cycles whenusing 1M LiTFSI electrolyte without adding lithium nitrate. FIG. 3further shows that LiHFDF can effectively improve the cycle performanceof metal-sulfur battery.

3. Test the batteries prepared by Embodiment 24 and Comparative example17 for 500 cycles at current density of 0.5 C and 1 C, and the testresults are shown in FIG. 4 and FIG. 5.

It can be seen from FIG. 4 that the coulombic efficiency of the batteryprovided by the present disclosure using LiTFSI electrolyte withoutlithium nitrate was only 82% after 200 cycles at a current density of0.5 C; while the coulombic efficiency of the battery still reached 92%after 200 cycles by adding 0.2M LiHFDF into LiTFSI electrolyte withoutlithium nitrate, indicating that LiHFDF can effectively improve thecoulombic efficiency of the battery. It can be seen from FIG. 5 that, inthe absence of lithium nitrate, the coulombic efficiency of the batteryusing LiTFSI electrolyte was 82% at the current density of 1 C; whilethe coulombic efficiency of the battery increased to 95% after addingLiHFDF, which further indicated that LiHFDF could effectively improvethe coulombic efficiency of the battery.

4. Test the cycle performance of the metal-sulfur batteries prepared byEmbodiments 1-25 and Comparative examples 1-17, and the test resultswere shown in Table 1.

TABLE 1 Positive Negative Battery capacity corresponding to electrodeelectrode Electrolyte Electrolyte cycle number (mAhg⁻¹) Sample materialmaterial solvent additive 1 10 100 500 Embodiment 1 C/S compositeLithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- 695 626 614 540(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimide;1 wt % LiNO₃ Embodiment 2 C/S composite Sodium DOL:DME = 1:1 1M sodium1,1,2,2,3,3- 530 515 460 352 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide Embodiment 3 C/S composite potassium DOL:DME= 1:1 1M potassium 1,1,2,2,3,3- 512 493 435 326 (Sulfur:Ketjen sheethexafluoropropane-1,3- Black = 1:3) disulfonimide Embodiment 4 C/Scomposite Lithium DOL:DME = 1:1 1.2M lithium 1,1,2,2,3,3- 705 680 630489 (Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3)disulfonimide; 1 wt % LiNO₃ Embodiment 5 C/S composite Lithium DOL:DME =1:1 1.3M lithium 1,1,2,2,3,3- 704 693 634 496 (Sulfur:Ketjen sheethexafluoropropane-1,3- Black = 1:3) disulfonimide; 1 wt % LiNO₃Embodiment 6 C/S composite Lithium DOL:DME = 1:1 1.4M lithium1,1,2,2,3,3- 705 710 658 523 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 7 C/S compositeLithium EC:DME = 1:1 1M lithium 1,1,2,2,3,3- 703 685 520 485(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimide;1 wt % LiNO₃ Embodiment 8 C/S composite Lithium FEC:DOL = 1:1 1M lithium1,1,2,2,3,3- 690 658 534 474 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 9 C/S compositeLithium FEC:DME = 1:1 1M lithium 1,1,2,2,3,3- 704 690 635 526(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimide;1 wt % LiNO₃ Embodiment 10 C/S composite Lithium VC:DME = 1:1 1M lithium1,1,2,2,3,3- 702 687 645 513 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 11 C/S compositeLithium PC:DME = 1:1 1M lithium 1,1,2,2,3,3- 698 680 634 521(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimide;1 wt % LiNO₃ Embodiment 12 C/S composite Lithium DEC:DME = 1:1 1Mlithium 1,1,2,2,3,3- 703 694 653 498 (Sulfur:Ketjen sheethexafluoropropane-1,3- Black = 1:3) disulfonimide; 1 wt % LiNO₃Embodiment 13 C/S composite Lithium EMC:DME = 1:1 1M lithium1,1,2,2,3,3- 695 640 643 498 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 14 C/S compositeLithium PS:DME = 1:1 1M lithium 1,1,2,2,3,3- 703 695 613 491(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimide;1 wt % LiNO₃ Embodiment 15 C/S composite Lithium PA:DME = 1:1 1M lithium1,1,2,2,3,3- 682 670 536 357 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 16 C/S compositeLithium DOL:DME = 1:1 1M lithium 1,1- 704 659 534 347 (Sulfur:Ketjensheet difluoromethane- Black = 1:3) disulfonimide; 1 wt % LiNO₃Embodiment 17 C/S composite Lithium DOL:DME = 1:1 1M lithium 1,1,2,2-715 670 540 379 (Sulfur:Ketjen sheet tetrafluoroethane-1,2- Black = 1:3)disulfonimide; 1 wt % LiNO₃ Embodiment 18 C/S composite Lithium DOL:DME= 1:1 1M lithium 1,1,2,2,3,3,4,4- 716 680 640 480 (Sulfur:Ketjen sheetoctafluorobutane-1,4- Black = 1:3) disulfonimide; 1 wt % LiNO₃Embodiment 19 C/S composite Lithium DOL:DME = 1:1 1M lithium1,1,2,2,3,3- 723 688 614 413 (Sulfur:Ketjen sheet hexafluoropropane-1-Black = 1:3) sulfonyl-3- sulfonimide; 1 wt % LiNO₃ Embodiment 20 C/Scomposite Lithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- 715 686 613 402(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimideEmbodiment 21 C/S composite Lithium DOL:DME = 1:1 1M lithium1,1,2,2,3,3- 713 689 628 489 (Sulfur:Ketjen sheet hexafluoropropane-1,3-Black = 1:3) dicarboxyimide; 1 wt % LiNO₃ Embodiment 22 C/S compositeLithium DOL:DME = 1:1 1M lithium 1,2,3,3- 671 661 568 451 (Sulfur:Ketjensheet tetrafluoro-1-propene- Black = 1:3) 1,3-disulfonimide Embodiment23 C/S composite Lithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- 671 667578 456 (Sulfur:Ketjen sheet hexafluoropropane-1- Black = 1:3)carboxylic acid-3- sulfonimide; 1 wt % LiNO₃ Embodiment 24 C/S compositeLithium DOL:DME = 1:1 1M lithium 708 740 416 359 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide + 0.2M lithium1,1,2,2,3,3- hexafluoropropane-1,3- disulfonimide Embodiment 25 Nanosilicon Lithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- 2904 2812 27502051 sheet hexafluoropropane-1,3- disulfonimide; 1 wt % LiNO₃Comparative C/S composite Lithium DOL:DME = 1:1 1M lithium 690 642 463330 example 1 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3)sulfonimide; 1 wt % LiNO₃ Comparative C/S composite Sodium DOL:DME = 1:11M sodium 534 522 463 151 example 2 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide Comparative C/S compositePotassium DOL:DME = 1:1 1M potassium 476 454 307 214 example 3(Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimideComparative Nano silicon Lithium DOL:DME = 1:1 1M lithium 2800 2670 25141798 example 4 sheet bistrifluoromethane- sulfonimide; 1 wt % LiNO₃Comparative C/S composite Lithium DOL:DME = 1:1 1.2M lithium 704 675 589412 example 5 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3)sulfonimide; 1 wt % LiNO₃ Comparative C/S composite Lithium DOL:DME =1:1 1.3M lithium 703 679 576 403 example 6 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide; 1 wt % LiNO₃ ComparativeC/S composite Lithium DOL:DME = 1:1 1.4M lithium 689 676 571 394 example7 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimide; 1wt % LiNO₃ Comparative C/S composite Lithium EC:DME = 1:1 1M lithium 695670 510 428 example 8 (Sulfur:Ketjen sheet bistrifluoromethane- Black =1:3) sulfonimide; 1 wt % LiNO₃ Comparative C/S composite Lithium FEC:DOL= 1:1 1M lithium 699 649 529 429 example 9 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide; 1 wt % LiNO₃ ComparativeC/S composite Lithium FEC:DME = 1:1 1M lithium 678 660 595 421 example10 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimide; 1wt % LiNO₃ Comparative C/S composite Lithium VC:DME = 1:1 1M lithium 675650 578 432 example 11 (Sulfur:Ketjen sheet bistrifluoromethane- Black =1:3) sulfonimide; 1 wt % LiNO₃ Comparative C/S composite Lithium PC:DME= 1:1 1M lithium 657 645 548 391 example 12 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide; 1 wt % LiNO₃ ComparativeC/S composite Lithium DEC:DME = 1:1 1M lithium 667 646 516 331 example13 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimide; 1wt % LiNO₃ Comparative C/S composite Lithium EMC:DME = 1:1 1M lithium677 645 508 323 example 14 (Sulfur:Ketjen sheet bistrifluoromethane-Black = 1:3) sulfonimide; 1 wt % LiNO₃ Comparative C/S composite LithiumPS:DME = 1:1 1M lithium 669 651 504 312 example 15 (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide; 1 wt % LiNO₃ ComparativeC/S composite Lithium PA:DME = 1:1 1M lithium 674 660 510 308 example 16(Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimide; 1 wt% LiNO₃ Comparative C/S composite Lithium DOL:DME = 1:1 1M lithium 701562 363 164 example 17 (Sulfur:Ketjen sheet bistrifluoromethane- Black =1:3) sulfonimide

It can be seen from the test results in Table 1 that compared with otherexisting metal-sulfur batteries, the metal-sulfur battery provided bythe present disclosure shows better cycle performance, can effectivelyinhibit the formation of metal dendrites, and reduce the capacity lossduring the charging and discharging process of the battery.

5. Test the electrochemical cycle stability of the batteries prepared byEmbodiments 26-28 and Comparative examples 18-20 using Xinwei batterytesting system. The main test contents include the detection ofcoulombic efficiency, interface impedance EIS and charge-discharge curveof the lithium sheet half battery, and the test results are shown inFIG. 6-FIG. 13.

It can be seen from FIG. 9, FIG. 11 and FIG. 13 that the electrolyteprovided by the present disclosure can effectively inhibit thegeneration of lithium dendrites and the amount of dead lithium, and thecoulombic efficiency is still greater than 96% after more than 100cycles.

It can be seen from FIG. 6, FIG. 10 and FIG. 12 that the electrochemicalimpedance of the battery provided by the present disclosure isrelatively low, and the interfacial impedance is small, which is mainlydue to the fact that its electrolyte effectively inhibits the generationof lithium dendrites and dead lithium. In the comparative example, theinterfacial impedance of LiTFSI electrolyte is relatively large, whichis mainly due to the generation of a large number of lithium dendritesor dead lithium, resulting in an increase in the number of interfacesand an increase in the interfacial impedance.

It can be seen from FIG. 7 and FIG. 8 that the polarization voltage ofthe battery provided by the present disclosure is small during chargingand discharging, which can directly prove that the electrolyte providedby the present disclosure has an unexpected effect in inhibiting theformation of lithium dendrites.

Embodiments 29-36

Embodiments 29-36 are used to illustrate the metal-sulfur battery andits preparation method disclosed in the present application, it was thesame as Embodiment 1 except that:

the adopted positive electrode material, negative electrode material,electrolyte solvent and electrolyte additive are shown in Embodiments29-36 of Table 2.

Comparative Examples 21-24

Comparative examples 21-24 are used to contrastively illustrate themetal-sulfur battery and its preparation method disclosed in the presentapplication, it includes most of the steps of Embodiment 1, with thefollowing differences:

the adopted positive electrode material, negative electrode material,electrolyte solvent and electrolyte additive are shown in Comparativeexample 21-24 of Table 2.

TABLE 2 Positive Negative electrode electrode Electrolyte ElectrolyteSample material material solvent additive Embodiment 1 C/S compositeLithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- (Sulfur:Ketjen sheethexafluoropropane-1,3- Black = 1:3) disulfonimide; 1 wt % LiNO₃Embodiment 29 C/S composite Sodium DOL:DME = 1:1 1M sodium 1,1,2,2,3,3-(Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3) disulfonimideEmbodiment 30 C/S composite Potassium DOL:DME = 1:1 1M potassium1,1,2,2,3,3- (Sulfur:Ketjen sheet hexafluoropropane-1,3- Black = 1:3)disulfonimide Embodiment 31 C/S composite Lithium FEC:DOL = 1:1 1Mlithium 1,1,2,2,3,3- (Sulfur:Ketjen sheet hexafluoropropane-1,3- Black =1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 32 C/S composite LithiumDOL:DME = 1:1 1M lithium 1,1- (Sulfur:Ketjen sheet difluoromethane-Black = 1:3) disulfonimide; 1 wt % LiNO₃ Embodiment 33 C/S compositeLithium DOL:DME = 1:1 1M lithium 1,1,2,2,3,3- (Sulfur:Ketjen sheethexafluoropropane-1,3- Black = 1:3) dicarboxyimide; 1 wt % LiNO₃Embodiment 34 C/S composite Lithium DOL:DME = 1:1 1M lithium 1,2,3,3-(Sulfur:Ketjen sheet tetrafluoro-1-propene-1,3- Black = 1:3)disulfonimide Embodiment 35 C/S composite Lithium DOL:DME = 1:1 1Mlithium 1,1,2,2,3,3- (Sulfur:Ketjen sheet hexafluoropropane-1- Black =1:3) carboxylic acid-3- sulfonimide; 1 wt % LiNO₃ Embodiment 36 C/Scomposite Lithium DOL:DME = 1:1 1M lithium (Sulfur:Ketjen sheetbistrifluoromethane- Black = 1:3) sulfonimide + 0.2M lithium1,1,2,2,3,3- hexafluoropropane-1,3- disulfonimide Comparative C/Scomposite Lithium DOL:DME = 1:1 1M lithium example 1 (Sulfur:Ketjensheet bistrifluoromethane- Black = 1:3) sulfonimide; 1 wt % LiNO₃Comparative C/S composite Sodium DOL:DME = 1:1 1M sodium example 21(Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimideComparative C/S composite Potassium DOL:DME = 1:1 1M potassium example22 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimideComparative C/S composite Lithium FEC:DME = 1:1 1M lithium example 23(Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3) sulfonimide; 1 wt% LiNO₃ Comparative C/S composite Lithium PA:DME = 1:1 1M lithiumexample 24 (Sulfur:Ketjen sheet bistrifluoromethane- Black = 1:3)sulfonimide; 1 wt % LiNO₃

Performance Test

1. After the metal-sulfur batteries prepared by Embodiment 1 andComparative example 1 were cycled for 5 times, the batteries weredisassembled, and the pictures of battery pole piece and TEM and EDX ofthe battery materials were extracted and shown in FIG. 14. Pictures a, band c in the upper half of FIG. 14 are the pictures of the battery polepiece, TEM and EDX of the battery materials of the metal-sulfur batteryprovided by Embodiment 1; Pictures d, e and f in the lower half of FIG.14 are the pictures of the battery pole piece, TEM and EDX of thebattery materials of the metal-sulfur battery provided by Comparativeexample 1.

It can be seen by comparing the pictures in FIG. 14 that the electrolyteprovided by the present disclosure was used in the battery of Embodiment1, and the sulfur on the separator of the battery was obviously lessthan that of using LiTFSI electrolyte after five cycles of charging anddischarging. The above indicates that the electrolyte provided by thepresent disclosure can inhibit the dissolution of sulfur during thecharging and discharging process. It can be seen from the picture of TEMthat a thick SEI film was formed on the surface of the battery materialby using the electrolyte provided by the present disclosure, and it canbe seen from the picture of EDX that this SEI film was mainly composedof chemical substances containing F.

2. The test results of Embodiment 29 and Comparative example 21 areshown in FIG. 15. Picture a shows the sulfur dissolution of Embodiment29 after five cycles, and picture b shows the sulfur dissolution ofComparative example 21 after five cycles. It can be seen from thepictures that the sulfur content on the separator using cyclic sodium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide is obviously less thanthat on the separator using noncyclic sodium bis(trifluoromethylsulfonyl) amino, which indicates that cyclic sodium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide can inhibit thedissolution of sulfur.

3. The test results of Embodiment 30 and Comparative example 22 areshown in FIG. 16. Picture a shows the sulfur dissolution of Embodiment30 after five cycles, and picture b shows the sulfur dissolution ofComparative example 22 after five cycles. It can be seen from thepictures that the sulfur content of the separator using cyclic potassium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide is obviously less thanthat of the separator using noncyclic potassiumbistrifluoromethanesulfonimide, which indicates that cyclic potassium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide can inhibit thedissolution of sulfur.

4. The test results of Embodiment 31 and Comparative example 23 areshown in FIG. 17. Picture a shows the sulfur dissolution of Embodiment31 after five cycles, and picture b shows the sulfur dissolution ofComparative example 23 after five cycles. It can be seen from thepictures that, in the solvent of FEC:DME=1:1, the sulfur content on theseparator using cyclic lithium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide is obviously less thanthat on the separator using noncyclic lithiumbistrifluoromethanesulfonimide, which indicates that cyclic lithium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide can also inhibit thedissolution of sulfur in the fluorinated solvent.

5. The test results of Embodiment 32 and Comparative example 24 areshown in FIG. 18. Picture a shows the sulfur dissolution of Embodiment32 after five cycles, and picture b shows the sulfur dissolution ofComparative example 24 after five cycles. It can be seen from thepictures that, in the solvent of DOL:DME=1:1, the sulfur content on theseparator using 1M cyclic lithium 1,1-difluoromethane-disulfonimide isobviously less than that on the separator using noncyclic lithiumbistrifluoromethanesulfonimide, which indicates that other cycliclithium sulfonimide can also inhibit the dissolution of sulfur.

6. FIG. 19 are pictures of sulfur dissolution on the battery separatorsof Embodiments 33-36 (pictures a-d in FIG. 19) and Comparative example 1(picture e in FIG. 19) after five cycles. It can be seen from thepictures that using cyclic lithium carbodiimide, unsaturated lithiumsulfonimide, and cyclic lithium imide containing carboxyacyl andsulfonyl as lithium salt for electrolyte, and using lithium1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide as additive forelectrolyte can both inhibit the dissolution of sulfur.

The above are only preferred embodiments of the present disclosure, andnot intended to limit the present disclosure. Any modifications,equivalent substitutions and improvements made within the spirit andprinciples of the present disclosure shall be included in the protectionscope of the present disclosure.

1. A metal-sulfur battery, comprising a positive electrode material, anegative electrode material and an electrolyte, the positive electrodematerial comprises one of elemental sulfur and S-based compound; theelectrolyte comprises a solvent and an electrolyte salt; and theelectrolyte salt comprises one or more salts represented by structuralformulas 1-3:

wherein, R₁ is selected from S or Se; R₂ is selected from C, Si, Ge orSn; M₁ is selected from N, B, P, As, Sb or Bi; M₂ is selected from Li,Na, K, Ru, Cs, Fr, Al, Mg, Zn, Be, Ca, Sr, Ba or Ra; R₃ is selected froma carbon chain or an aromatic ring with part or all of hydrogensubstituted by other elements or groups.
 2. The metal-sulfur battery ofclaim 1, wherein the content of the electrolyte salt is 0.01M˜10M. 3.The metal-sulfur battery of claim 1, wherein in structural formulas 1-3,R₃ is selected from a saturated carbon chain containing 1-4 carbons, anunsaturated carbon chain containing 1-4 carbons or an aromatic ring,with part or all of hydrogen substituted by a halogen element or ahalogenated hydrocarbyl group.
 4. The metal-sulfur battery of claim 1,wherein the electrolyte salt comprises one or more of the followingcompounds:


5. The metal-sulfur battery of claim 1, wherein the positive electrodematerial is a sulfur/carbon composite.
 6. The metal-sulfur battery ofclaim 1, wherein the positive electrode material is a ketjenblack/sulfur composite.
 7. The metal-sulfur battery of claim 1, whereinthe electrolyte further comprises a nitrate, and the mass percentage ofthe nitrate is 0.1%-5% based on the mass of the electrolyte being 100%.8. The metal-sulfur battery of claim 1, wherein the negative electrodematerial comprises one or more of elemental lithium, elemental sodium,elemental potassium, elemental aluminum and elemental magnesium.
 9. Themetal-sulfur battery of claim 1, further comprising a separatorinterposed between the positive electrode material and the negativeelectrode material.
 10. The metal-sulfur battery of claim 1, wherein themetal-sulfur battery is a lithium-sulfur battery.
 11. The metal-sulfurbattery of claim 1, wherein the solvent is selected from one or more ofa fluorinated solvent, ethylene glycol dimethyl ether, 1,3-dioxolane,propylene sulfite and methyl propionate.
 12. The metal-sulfur battery ofclaim 11, wherein the fluorinated solvent comprises one or more offluoroethylene carbonate, 3,3,3-fluoroethyl methyl carbonate and1,1,2,2-tetrafluoroethyl-2′,2′,2′-trifluoroethyl ether.
 13. Themetal-sulfur battery of claim 1, wherein the electrolyte salt furthercomprises one or more of LiPF₆, LiBF₄, LiBOB, LiClO₄, LiCF₃SO₃, LiDFOB,LiN(SO₂CF₃)₂ and LiN(SO₂F)₂.